1. Field of the Invention:
This invention relates to the field of antivibration isolation devices, and in particular to the elastic parts used for this purpose in automotive vehicles, and in which a great static and dynamic flexibility of these elastic connections comes into conflict with the permanent or temporary forces exerted. In particular the forces between the chassis and the steering elements of the suspension or the connection to the ground.
2. Description of the Prior Art:
A first family of devices, currently used to solve this problem, filters vibrations in the median position by means of rubber blocks which are connected on one side to the chassis, or at least pressed against the fastening frames, and on the other side to the assembly to be isolated, such as a cross member of the frame supporting the rear axle of the vehicle. Extreme forces, or forces which exceed a certain value, are transmitted by contact between the lateral walls, which are normally free to move, and a rigid casing, generally made of metal, enclosing the deformable part, and thereby serving as a limit stop. The progressive nature of this contact regulates the transition from the zone in which a great deal of filtering takes place, before deformation, to the zone which is necessarily ten to fifty times more rigid, when forces are exerted, e.g. longitudinal forces during braking, or transverse forces during lateral steering. The objective is not to exceed several millimeters between the two positions, so as not to introduce instability in the steering of the vehicle. An example would be a rigidity of 15 or 25 daN per mm, and stop forces reaching 250 or 300 daN, without prohibitive travel. The principle of these applications is described in French Pat. No. 898.055 assigned to Getefo.
A second family of devices is used, in particular as an anti-torque strut of a drive unit, by connecting the body of a strut, which is bonded to or surrounded by an elastomer block forming an elastic articulation around a rod, but enclosing voids or cells within this block. When moderate forces, e.g., motor torque, are exerted, the form factor, i.e., the ratio of the free surface of the elastomer to its blocked surface on each rigid frame allows high deformability with low rigidity. On the other hand, once the cells are closed by flattening the free surfaces in the enclosing voids or cells within this block, high rigidity is obtained by means of the elastic layers which are effectively enclosed, thereby taking advantage of the fact that the rubber is practically, virtually, volumetrically incompressible.
One example of this mounting is described in the General Motors Corporation French Patent No. 2,453,746.
A third means of achieving high rigidity in a single privileged or preferred direction is to block the deformity by means of a rigid support in this direction. This means has the disadvantage of limiting the antivibration filtering, in particular, at least in this direction.
British Pat. No. 901,454 to H. D. Munson describes such solid stops, in contact with the fastening plates of a rubber sandwich. Lateral movement is permitted by spherical stops which rotate on their supports. Of course, when large forces are exerted, the elastic filtering is short circuited, in particular, by the two solid contacts. In spite of the fact that the support surface is restricted, it has virtually the rigidity of metal in the direction of compression.
All of the above-cited patents are incorporated herein by reference as if the entire contents thereof were fully set forth herein.